Image exposure head and image forming apparatus

Abstract

An exposure head for forming an image of a first resolution corresponding to an arrangement interval of a plurality of lower electrodes in a crossing direction or an image of a second resolution lower than the first resolution. A circuit portion includes an image data storage portion that is arranged on the substrate together with a plurality of lower electrodes and converts input image data into image data according to the resolution. By this, the same exposure head can be used for both high resolution images and low resolution images without degrading the image quality.

What is claimed is: 
     
       1. An exposure head comprising:
 a plurality of light-emitting devices configured to expose a rotationally driven photosensitive member with light, wherein each of the plurality of light-emitting devices includes:
 a first substrate, 
 a first electrode layer including a plurality of electrodes that are (i) two-dimensionally arranged in a rotational direction of the photosensitive member and in the a direction of a rotational axis of the photosensitive member, and which (ii) are separately formed on the first substrate, 
 a light-emitting layer laminated on the first electrode layer and configured to emit light when a voltage is applied, 
 a light-emitting region including a second electrode layer capable of transmitting light, the light-emitting region being provided on a side of the light-emitting layer that is opposite to a side on which the first substrate and the first electrode layer are provided, the light-emitting region corresponding to the plurality of electrodes of the first electrode layer; and 
 
 a second substrate on which the first substrates of the plurality of light-emitting devices are arranged at positions different from each other in an intersecting direction intersecting the rotational direction of the photosensitive member, with odd-numbered first substrates and even-numbered first substrates being at different positions in the rotational direction of the photosensitive member, and with the first substrates of the plurality of light-emitting devices being arranged so as to have overlapping portions in which respective end portions of the first substrates adjacent to each other overlap each other in the intersecting direction, 
 wherein a driving portion including a converting portion is provided on each of the first substrates together with the light-emitting region, the converting portion being configured to convert received image data into the image data corresponding to a resolution. 
 
     
     
       2. An exposure head according to  claim 1 , wherein, when the resolution is a first resolution and when a latent image is to be formed on the photosensitive member at a second resolution that is lower than the first resolution, the converting portion of each of the plurality of light-emitting devices converts the received data so that two adjacent electrodes of the first electrode layer in the light-emitting region of each of the plurality of light-emitting devices have the same image data. 
     
     
       3. An exposure head according to  claim 2 , wherein the converting portion of each of the plurality of light-emitting devices includes a memory circuit group having a plurality of memory circuits configured to hold the image data for driving the plurality of electrodes in the first electrode layer,
 wherein the driving portion of each of the plurality of light-emitting devices includes a pulse signal generating portion group having a plurality of pulse signal generating portions configured to generate pulse signals on the basis of image data held in the memory circuit, 
 wherein each pulse signal generating portion group generates a pulse signal based on the image data held in the memory circuit group, and 
 wherein each memory circuit group holds the same image data in two adjacent memory circuits when the latent image is formed on the photosensitive member at the second resolution. 
 
     
     
       4. An exposure head according to  claim 2 , wherein each light-emitting region of the plurality of light-emitting devices includes two rows of light-emitting regions, and
 wherein, when the latent image is to be formed on the photosensitive member at the second resolution, each converting portion of the plurality of light-emitting devices converts the received data such that the electrodes included in two adjacent first electrode layers have the same image data, and such that the electrodes included in the two adjacent first electrode layers correspond to predetermined positions in the intersecting direction of the two rows of light-emitting regions that emit light on the basis of the same image data. 
 
     
     
       5. An exposure head according to  claim 4 ,
 wherein a first pulse signal generating portion group generates a first pulse signal on the basis of the image data held in a first memory circuit group provided corresponding to the a first light-emitting region, 
 wherein the second pulse signal generating portion group generates a second pulse signal at a different timing from the timing at which the first pulse signal is generated, on the basis of the image data held in a second memory circuit group provided corresponding to a second light-emitting region different from the first light-emitting region, and 
 wherein, when the latent image is formed on the photosensitive member at the second resolution, the first memory circuit group and the second memory circuit group hold the same image data in two adjacent memory circuits. 
 
     
     
       6. An exposure head according to  claim 1 , wherein the first substrate is a silicon substrate. 
     
     
       7. An image forming apparatus comprising:
 a photosensitive member; 
 an exposure head according to  claim 1 , the exposure head being configured to expose the photosensitive member to form an electrostatic latent image; 
 a developing unit configured to develop the electrostatic latent image with toner to form a toner image; and 
 a transfer unit for transferring the toner image onto a recording sheet.